Clarify Fog env var in README.md
Amended command in README.md to match real cmd

This commit amends a command used in README.md as an example in order to match a real-world command.
Uses vcloud-launch cmd

vcloud-query is being moved in to vcloud-core soon, so this change keeps the readme up-to-date for longer
Merge pull request #105 from alphagov/amend-fog-envvar

Clarify Fog env var in README.md